The present invention relates to a tool-holding chuck for equipping a rotating machine, in particular a drill.
Conventionally, a chuck includes a body having an axis and including a rear part intended to be fixed to a driver shaft of the machine and a front part in which forward-converging housings are formed, jaws each mounted slidably in a housing of the body and having an external thread, a nut mounted to rotate on the body and having an internal thread engaged with the external thread of the jaws, and a sleeve having an inner wall which cooperates with the nut so as to rotate it with respect to the body and thus move the jaws between a tool-clamping position and a released position.
The advantage of chucks of this type is that they allow a tool to be clamped without requiring the use of a key, while at the same time avoiding untimely opening of the chuck, particularly during percussion work.
It is known practice to provide radial and/or axial locking means on such chucks.
Radial locking means make it possible to prevent the nut from rotating with respect to the body when the jaws are in the clamping position. They can be actuated automatically and in a manner which is transparent to the operator during the clamping and releasing phases of the chuck, for example using the same rotational movement of the sleeve about the body which enables the chuck to be clamped and released.
Axial locking means for their part, when in the locked position, are aimed at preventing the radial locking means from unlocking. Once the chuck has been locked radially, the operator is required to move the sleeve in the axial direction, generally from the front to the rear of the chuck, to achieve locking. In the same way, when opening the chuck, the operator is first required to move the sleeve in the axial direction, generally from the rear to the front of the chuck, to unlock the latter before being able to release the chuck radially.
To make total locking available, chucks may be equipped with two combined locking systems, one radial and one axial.
However, it is clearly apparent that these two locking systems must be employed in a specific order so that each of them can perform its task perfectly. The very principle of these systems demands that the radial locking system be triggered first and that the axial locking system be triggered in a second step.
In fact, if the axial locking system is triggered first, the radial locking system will be unable to be triggered since the sleeve will then be inhibited from rotating with respect to the body. Moreover, if the axial locking system is triggered first, that may result in damage to the axial locking system since the operator will seek to turn the sleeve to trigger the radial locking means even though the said sleeve will have already been immobilized rotationally.
Actuating the axial locking system first may also prove to be dangerous for the operator. Specifically, when the operator manoeuvres the chuck with the aid of the drill, particularly a cordless drill, if the axial locking system is triggered first, the sleeve will be automatically and abruptly inhibited from rotating with respect to the body of the chuck. Thus, the operator runs the risk of injuring his hand.